1. Field of the Invention
The invention relates to printing carriers for transferring confidential information with a transparent film layer onto the front side of which the confidential information can be printed and wherein a concealing means, which complicates the capability to identify the confidential information on the film layer is present behind the film layer.
2. Description of the Prior Art
Printing carriers comprising confidential information, e.g., personal identification numbers of bank or credit cards are often sent via mail. The confidential information must thereby be protected in such a manner that it cannot be read by third parties, or also by the sender (e.g. bank employees). The receiver for whom the confidential information is intended is also to be able to identify whether the confidential information has been read by third parties.
Printing carriers in the form of standard forms comprising a transparent film, which can be imprinted by means of a laser printer or an ink jet printer and which is glued on top of a concealing means, are known from EP 1 293 359, WO 00/54984 and WO 99/24267. A transparent separating layer, generally a silicon layer, is located between the film and the concealing means. The confidential information is printed onto the transparent film and cannot be read in transmitted light due to the concealing means located therebelow. Under normal circumstances, the confidential information can thus not be read by bank employees, e.g., who print and package the standard form. The confidential information can be identified only when the end user separates the film and the concealing means from one another at the separating layer.
However, depending on the state of the toner or of the ink, the confidential information is capable of being identified under specularly reflected light in spite of the concealing means with the known embodiments.